Diurnal Vaeiations for the Vertical Component of Magnetic Force. Iv 



Tliroughout the year, therefore, the greatest effect of disturbance in increasing the vertical component occurs 

 near 6^ p.m. or ahout the epoch of the maximum for the mean value, No. 100. 



'2d, The greatest effect of disturbance in diminishing the vertical component occurs 



In Dec. Jan. Feb. 



About 2'^ 30m A.M. 



March, April. 

 Ih 40m A.M. 



May, June. 

 2^ 50m A.M. 



.July, Aug. 

 2h 45ra A.M. 



Sept. Oct. Nov. 

 3'^ 30™ A.M. 



The greatest effect in diminishing the vertical component occurs throughout the year between \^ and 3J'' 

 A.M., or rather after the epoch of the principal minimum for the mean value, No. 100. Irregular disturbance, 

 therefore, has the same effect on the value of the vertical component as the cause producing the regular diurnal 

 variation. 



3d, The effect of disturbance on the vertical component is zero 



In Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Nov. 



About ll^^ A.M. & gfl' P.M. \0^ A.M. & 91" P.M. 9^^ A.M. & lO^l^ P.M. lO^^ A.M. & 9fh p.m. Q^^ A.M. & 9'^ P.M. 



The effect of disturbance on the hourly mean appears to be zero about the time the sun is on the magnetic meridian. 



Diurnal Variation of Frequency of the Positive Departures from the Hourly Mean Positions. — The number 

 of observations which were in excess of the hourly mean for each month in 1844 and 1845 having been ob- 

 tained, the means for groups of months were taken, and the following Table was formed. 



Table 52. — Numbers in 100 Observations of the Vertical Component of Magnetic Force which were 

 greater than the corresponding Hourly Means, deduced from all the Hourly Observations in 1844 

 and 1845. 



Mak. 



Nov. 



Feb. 



May. 



Aug. 





Mak. 



Nov. 



Feb. 



May. 



Aug. 





Mean 



Dec. 



March. 



June. 



Sept. 



Year. 



Mean 



Dec. 



March. 



June. 



Sept. 



Year. 



Time. 



Jan. 



April. 



July. 



Oct. 





Time. 



Jan. 



April. 



July. 



Oct. 





li. 111. 

 12 13 



55-7 



70-1 



58-2 



1 

 67-1 



62-8 



li. m. 



13 



46-8 



45-5 



49-4 



40-5 



45-5 



13 13 



56-3 



66-2 



58-2 



67-1 



61-9 



1 13 



47-5 



46-1 



51-9 



40-5 



46-5 



14 13 



62-0 



71-4 



620 



67-1 



65-6 



2 13 



43-0 



42-9 



54-4 



41-8 



45-5 



15 13 



58-2 



70-8 



62-0 



66-5 



64-4 



3 13 



34-8 



36-4 



51-3 



39-2 



40-4 



16 13 



58-9 



72-7 



63-3 



64-6 



64-9 



4 13 



34-8 



35-1 



46-8 



39-2 



39-0 



17 13 



570 



70-1 



62-0 



65-8 



63-7 



5 13 



32-3 



33-1 



45-6 



35-4 



36-6 



18 13 



570 



64-9 



58-9 



66-5 



61-8 



6 13 



29-7 



35-7 



48-1 



35-4 



37-2 



19 13 



53-2 



57-8 



55-7 



58-2 



56-2 



7 13 



32-9 



38-3 



46-2 



41-1 



39-6 



20 13 



51-3 



591 



53-8 



54-4 



54-6 



8 13 



38-6 



45-5 



49-4 



50-0 



45-9 



21 13 



53-8 



56-5 



57-0 



50-6 



54-5 



9 13 



44-3 



54-5 



52-5 



62-0 



53-3 



22 13 



53-8 



52-6 



53-2 



51-9 



52-9 



10 13 



53-8 



60-4 



53-8 



62-7 



57-7 



23 13 



50-0 



50-0 



48-7 



48-7 



49-3 



11 13 



570 



64-3 



54-4 



68-4 



610 



104. The following are the epochs of maximum and minimum frequency of the positive departures for each 

 quarter. 



I Nov. Dec. Jan. Feb. Mar. April. May, June, July. Aug. Sept. Oct. 



11'' P.M. — 2l» A.M. 



Maximum, 

 Minimum, 



5*' P.M. 



2h_4h A.M. 



51' 



P.M. 



2"— 5" A.i 



5'' P.M. 



llh P.M. Qh ^^j^j_ 



5f h P.M. 



It appears, therefore, that the number of positive departures from the mean of all the observations for the 

 hour is least about 5^ p.m., or about the time that the effect of disturbance in increasing the hourly mean is 

 greatest, and that the number is greatest when the effect of disturbance in diminishing the hourly mean is least. 

 No. 103 : the effect of disturbance on the hourly mean position is so considerable when compared with the 

 whole diurnal variation, that it is evident that the number of departures from the undisturbed positions must 

 have their maximum about b^ p.m. and their minimum about 2^ — 3'' a.m. 



Diurnal Variation of the Mean Differences of the Value of the Vertical Component from its Monthly Mean 

 Value at the corresponding Hour. — Table 53 has been formed from Table LIII., for 1844, p. 387, and 

 Table XLIII., p. 24 of this volume, in the manner already described. No. 43, for Table 18. 



MAG. AND MET. OBS. 1845 AND 1846. O 



